Electrochemical cells have been used for detection of toxic gases since the 1970's in, for example, fixed location instrumentation for infrastructure (such as buildings and parking garages) and portable safety and inspection equipment used in transportation. For example, see Stetter, J. R., “Instrumentation to Monitor Chemical Exposure in the Synfuel Industry,” Annals American Conf. of Governmental and Industrial Hygienists, 11, 225-269, (1984). These sensors may be desirable in ambient monitoring applications because of their accuracy at low detection levels, selectivity, linearity, and power requirements. Industrial-grade electrochemical cells can cost the customer over $25 each and even several hundred dollars without any electronics, even when manufactured in high volumes. This cost can significantly increase the cost of gas monitors and detectors, and can leave manufacturers with few cost-effective options to create ultra-cheap, yet high performance gas detectors. For example, high quality, accurate devices for sensing carbon monoxide and triggering an alarm in the presence of excessive concentrations of carbon monoxide (CO) that may be hazardous to life or health are presently available for many industrial applications, but such devices are still too costly for use in most homes.
As a result, less expensive sensors with much lower performance are chosen to meet high volume consumer product cost goals, resulting in lower performance and a sacrifice of needed safety and health protection for the consumer. Additional consumer, medical, and industrial applications will be made available with a significant reduction in the cost and dimensions of electrochemical gas sensors. Other prior art gas sensors may use a liquid proton conductor where the outside surfaces of the sensing and counter electrodes of the sensor are coated by NAFION™ layers. NAFION™ material is subject to freezing at 0 degrees (° C.)., hindering operation of a sensor coated by NAFION™ material at temperatures of 0° C. and below. Further, the lifetime of these sensors can range from about 6-12 months due to rapid drying of the liquid electrolyte. Thus, the sensor requires maintenance due to liquid electrolyte evaporation, leakage, and/or corrosion. In addition, the sensors can have significant manufacturing costs and be relatively large, sometimes with large electrolyte or water reservoirs, which make integration of these sensors into modern equipment or small personal monitors difficult.
Another prior art gas sensor uses a design incorporating proton conductors, one type of electronically conductive metal catalyst for the sensing electrode, and a different type of electronically conductive metal catalyst for the counter electrode. This configuration allows the sensing electrode to decompose a gas to produce protons and electrons, while the counter electrode exhibited no activity to decompose the gas. The result is a Nernst potential between the two electrodes, which can be used to detect a target gas. However, issues that could result from such a design include the gas reaction being carried out slowly or interfering reactions occurring on one or the other electrode surface. Additionally, the response signal could be weak. Further, the Nernst potential may be difficult to zero in clean air and the calibration is limited to about 59 millivolts (mV) per decade of concentration. Again poor electrolyte or electrode stability over time can degrade performance of a potentiometric gas sensor which often operate better at a high temperature.
Thus, there is a need or potential benefit for a competitive electrochemical sensor that can cost less to manufacture in high volume, has high performance and small size, and that would create a new opportunity for companies to develop low-cost gas detectors that could be manufactured in high volumes, thus making high accuracy detectors, such as carbon monoxide detectors, much less expensive. This cost reduction, without loss in performance, could revolutionize and tremendously expand the use of gas detectors in their application, including home carbon monoxide monitors, automobile air quality monitors, and building ventilation and controls. In addition, new applications would become possible, including safety organizations that may desire to inexpensively protect or monitor a large area from toxic gases like carbon monoxide, and universities or scientific/environmental organizations wanting to study toxic gas levels over large areas. In addition, an electrochemical sensor that also can be small can be used in cell-phones to enable worldwide networks of CO and other gas monitors.
The traditional porous, composite electrode is comprised of 10-40% polytetrafluoroethylene (PTFE) by weight and 60-90% catalyst by weight. The traditional electrode has possible residual dispersing, surfactants and thickening agents. These residual components are chemically inert and electrochemically inert. These electrodes are cured and/or sintered near the melting point of PTFE, typically 290-310 C. This requires printing on substrates such as porous PTFE that can withstand the PTFE cure temperatures. The PTFE serves as a binder to hold the catalyst particles together in a porous bed. It also serves as the hydrophobic portion of the composite bed electrode to provide a proper environment for a triple-phase boundary. This triple-phase boundary is desirous for gas-phase amperometric sensors.
A need or potential benefit exists for high performance electrochemical sensors having thin and tiny form factors and low cost assembly.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements or signals, electrically, mechanically and/or otherwise. Two or more electrical elements may be electrically coupled but not be mechanically or otherwise coupled; two or more mechanical elements may be mechanically coupled, but not be electrically or otherwise coupled; two or more electrical elements may be mechanically coupled, but not be electrically or otherwise coupled. Coupling may be for any length of time, e.g., permanent or semi-permanent or only for an instant.
“Electrical coupling” and the like should be broadly understood and include coupling involving any electrical signal, whether a power signal, a data signal, and/or other types or combinations of electrical signals. “Mechanical coupling” and the like should be broadly understood and include mechanical coupling of all types.
The absence of the word “removably,” “removable,” and the like near the word “coupled,” and the like does not mean that the coupling, etc. in question is or is not removable.